The present invention relates to a display device. The display device of the present invention can be a liquid crystal display device, organic and inorganic electroluminescence (EL) display device, a plasma display device and the like, for example.
Conventionally, in liquid crystal display (LCD) devices, a tape carrier package (TCP) mode is mainly adopted for mounting of liquid crystal (LC) driving ICs to an LC panel. FIG. 17A is a perspective view diagrammatically showing a TCP-mode LCD device. This LCD device, denoted by 500, includes an LC panel 501, and gate TCPs 502, source TCPs 503 and external circuit boards 504 placed along the periphery of the LC panel 501. The gate TCPs 502 and the source TCPs 503 are respectively provided for supplying signals to gate signal lines and source signal lines of the LC panel 501. The external circuit boards 504 are provided for supplying external signals to the gate TCPs 502 and the source TCPs 503.
FIG. 17B is a perspective view diagrammatically showing one gate TCP 502/source TCP 503. Each of the gate TCPs 502 and the source TCPs 503 includes an LC driving IC 505, signal input wiring 507 and signal output wiring 508 formed on a flexible base 506. The signal input wiring 507 supplies external signals, such as image data signals, a power supply voltage for IC driving and a power supply voltage for counter electrode driving, to the LC driving IC 505. The signal output wiring 508 supplies signals output from the LC driving IC 505.
The signal input wiring 507 of each of the gate TCPs 502 and the source TCPs 503 is electrically connected to terminals on the external circuit board 504, which is a printed wiring board (PWB) placed outside the LC panel 501, to lead the external signals to the LC driving IC 505 from the terminals on the external circuit board 504.
FIG. 18 is a view demonstrating signal input of the TCP-mode LCD device. In the LCD device 500, signals are directly input into the individual source TCPs 503, for example, from the external circuit board 504. Therefore, a considerably large number of wiring lines must be formed on the external circuit board 504. To accommodate these wiring lines, some contrivance such as forming the external circuit board 504 as a multilayer structure is necessary, and this causes disadvantages such as complicating the fabrication process, increasing the cost and decreasing the reliability.
To overcome the problem of the conventional TCP mode described above, a “signal propagation mode” has been introduced, in which a signal is once supplied to one TCP and then propagated to the adjacent TCP sequentially. This mode is disclosed in Japanese Laid-Open Patent Publication No. 4-313731, No. 10-214858, No. 2001-056481 and No. 2002-287655 and Japanese Laid-Open Utility Model Publication No. 3-114820, for example.
The signal propagation mode will be described with reference to FIG. 19. FIG. 19 is a view demonstrating signal input of an LCD device adopting the signal propagation mode. Each TCP 601 includes an LC driving IC 602, signal input wiring 603 for supply of an external signal to the LC driving IC 602, signal output wiring 605 for supply of an image signal from the LC driving IC 602 to an LC panel 604, and relay wiring 606 for outputting an LC driving signal to the adjacent TCP 601.
In the LCD device described above, when an external signal is supplied to a first-stage LC driving IC 602a from an external circuit board 607 via the signal input wiring 603, an image signal corresponding to the supplied external signal is sent to the LC panel 604 via the first-stage LC driving IC 602a and the signal output wiring 605. At this time, part of the external signal input into the first-stage LC driving IC 602a is lead to the relay wiring 606, to be supplied to the signal input wiring 603 of the adjacent second-stage TCP 601b via connection wiring 608 running on the LC panel 604.
Therefore, once a signal is input into the first-stage TCP 601a from the external circuit board 607, part of the signal is output to a pixel of the LC panel 604 via the LC driving IC 602a of the TCP 601a. The remainder of the signal is sequentially propagated to the adjacent TCPs 601b, 601c and 601d via the relay wiring 606 of the respective TCPs 601 and the connection wiring 608 on the LC panel 604.
The LCD device of the signal propagation mode using the relay wiring 606 can widely reduce the number of wiring lines required for input of signals from the external circuit board 607 into the TCPs 601a, 601b, 601c and 601d. For the external circuit board 607 on which a large number of wiring lines must be formed, some contrivance such as giving multiple layers is made to accommodate the large number of wiring lines. In this situation, the reduction of the number of wiring lines can reduce the number of layers, and this leads to cost reduction of the external circuit board 607.
However, the wiring structure in the signal propagation mode disclosed in the above-mentioned publications and the like has the following problem. External image signals are input into the LC driving ICs of the respective TCPs via the same wiring line. That is, a composite signal composed of image signals for the respective LC driving ICs in the number equal to the number of TCPs is input into the same wiring line. This inevitably causes increase of the clock frequency and thus adversely affects electromagnetic interference (EMI). Therefore, adopting this wiring structure will be more difficult as the LCD device is higher in definition.